An analysis of microband orientation in a commercial purity aluminium alloy subjected to forward and reverse torsion...

High-resolution electron backscatter diffraction has been used to study the effects of strain reversal on the evolution of microbands in commercial purity aluminium alloy AA1200. Deformation was carried out using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300 degrees C and strain rate of 1 s(-1) to a total equivalent tensile strain of 0.5. In both cases, microbands were found in the majority of grains examined with many having microband walls with more than one orientation. For the forward/forward condition, the microband clusters were centred around -20 degrees and +45 degrees to the equivalent tensile stress axis, whereas for material subjected to a strain reversal, the clusters were at -65 degrees and -45 degrees . There was no evidence of microbands that were formed in the forward deformation step in the reversed material, which would suggest that a strain of 0.25 is sufficient to dissolve any microstructure history generated by the first step. Furthermore, the microbands within the strain-reversed material had a reduction in misorientation compared with the lineally strained material, suggesting that these microbands only formed at the onset of the second deformation step. This confirms that microband formation is complex and sensitive to strain path; however, it is still unclear to what extent microband formation is dependent on strain path history compared with the instantaneous deformation mode.